The state of Indiana this week reported the first novel influenza virus outbreak associated with a fair this season.

Following reports of ill swine and humans during a fair in Indiana from July 8–14, samples were taken from swine and humans. Twelve swine were randomly sampled by Indiana state animal health officials, tested at Indiana and Federal animal diagnostic laboratories, and found to be infected with swine influenza A (H3N2) viruses. Four people tested positive for influenza A (H3N2) variant virus. Genetic testing confirmed that the viruses found in humans and those found in swine in this situation are nearly identical and both have the M gene from the pandemic H1N1 virus. These cases bring the total number of detected infections with the H3N2v virus containing the pandemic M gene in the United States since 2011 to 17.

Type A influenza viruses commonly infect swine, causing outbreaks among swine herds. Most of the type A influenza viruses that infect swine are genetically very different from human (seasonal) influenza viruses, including currently circulating seasonal H3N2 viruses. While swine flu viruses seldom infect humans, such infections can and do occur. In fact, influenza viruses can spread both ways from swine to humans and from humans to swine.  

The four cases reported by Indiana occurred in people who were exhibiting swine, or family members of people who were exhibiting swine and were associated with swine contact. Previously, however, there have been H3N2v infections with no reported swine contact and instances of limited human-to-human transmission. The National Association of State Public Health Veterinarians has developed the “Compendium of Measures to Prevent Disease Associated with Animals in Public Settings, 2011″ to provide some preventive actions that are applicable to people raising swine, showing swine at fairs, or attending fairs.”

Studies conducted by CDC have indicated that children <10 years old would have little to no immunity against H3N2v, whereas adults may have some cross-protective immunity. Most cases of H3N2v have occurred in children at this time. Other people who are at higher risk for seasonal flu-related complications include people with asthma, diabetes, heart disease or neurological disorders.

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